The present invention relates to the field of manufacturing construction products, and, more particularly, to systems for making lightweight, high-strength, fire-resistant wallboard sheet, and/or moisture-resistant backerboard sheets.
Wallboard sheets are widely used in building construction to form partitions or walls of rooms, elevator shafts, stair wells, ceilings, etc. The sheets are typically fastened to a suitable supporting framework. The seams between sheets are covered to provide an even wall surface. The sheets may be readily cut to size by first scoring the face sheet, and then snapping the board about the score line. The wall may then be painted or covered with a decorative wall covering, if desired. Such wallboard sheets created from a gypsum core with outer face layers of paper, sometimes referred to as gypsum board or drywall, are well known.
Gypsum wallboard is typically manufactured by delivering a slurry or paste containing crushed gypsum rock onto a moving sheet of facing paper to which a second or top paper layer is then added to form a long board line. The board line permits the slurry to harden before being cut. The cut panels are heated in a kiln, before being packaged for storage and shipping.
Typically, such sheets are xc2xd or ⅝ inch thick and in conventional sizes of 4xc3x978 feet, such a gypsum wallboard sheet may weigh about 55-70 pounds. Accordingly, handling of such gypsum wallboards presents a significant task for construction personnel or wallboard xe2x80x9changersxe2x80x9d, particularly when such boards are secured overhead to form a ceiling. In addition, the fire resistance, thermal insulation and sound absorbing properties of conventional gypsum wallboard sheets may not be sufficient for some applications.
Another variation of gypsum wallboard is water-resistant drywall or xe2x80x9cgreenboardxe2x80x9d. The greenboard typically includes the same gypsum core, but includes a water-resistant facing so the water is less likely to penetrate, stain and/or decay the wall. Greenboard is typically used for walls in a moist or humid environment, such as a bathroom, for example. Such greenboard is not typically recommended as an underlayment for tile in the bathroom, for example, since water may penetrate the grout or (tracks between adjacent tiles and deteriorate the greenboard. U.S. Pat. No. 5,552,187 to Green et al. discloses the addition of a fibrous mat-faced gypsum board coated with a water-resistant resinous coating for greater durability in moist environments.
Yet another related conventional wallboard product to serve as an underlayment for wet areas is the concrete backerboard. For example, UTIL-A-CRETE(copyright) Backerboard from Bonsal is a precast cementitious backboard with glass mesh reinformcement. The board includes portland cement, fiber glass mesh and lightweight aggregate. The backerboard is more adapted to be used in areas subject to splashing or high moisture.
While the glass mesh face layers are typically secured to the surface of the backerboard after the core has been precast, continuous production is also disclosed in U.S. Pat. No. 5,221,386 to Ensminger et al. In addition, the mesh or reinforcing layers have also been embedded in the faces and edges of the backerboards.
Unfortunately, conventional cementitious backerboards may be more difficult to score and break to size. Moreover, since the backerboards include a core of cement, their density is considerably greater than even conventional gypsum wallboard. Accordingly, manufacturers may offer the backerboards in smaller sizes to be more readily handled by the installer, but such increases seams between sheets and also increases costs of installation. A typically-sized 4 foot by 8 foot sheet can weigh well over 100 pounds, which is very unwieldy especially in confined spaces.
In view of the foregoing background, it is therefore an object of the invention to provide a system for making wallboard or backerboard sheets which are relatively lightweight, strong, and which have good fire resistance, thermal insulation, and sound absorbing properties.
This and other objects, features and advantages in accordance with the present invention are provided by a system for making wallboard or backerboard sheets comprising a mixer for mixing materials for making aerated concrete, at least one face layer supply, and a former downstream from the mixer. The former is for forming core material having opposing first and second major surfaces and comprising aerated concrete, and for securing at least one face layer from the at least one face layer supply onto at least one of the first and second major surfaces of the core material. The system may also include a cutter downstream from the former for cutting the core material and at least one face layer secured thereto into a plurality of wallboard or backerboard sheets. The provision of aerated concrete for the core provides many key advantages over conventional gypsum wallboard sheets, and/or conventional backerboard sheets, such as gypsum greenboard or cementitious backerboard, for example.
In one class of embodiments, the former may further include an autoclave for curing the core material prior to securing the at least one face layer thereto. In another class, the former may further include an autoclave for curing the core material after securing the at least one face layer thereto.
In one particularly advantageous embodiment of the system, the former may include a mold downstream from the mixer for receiving the materials for making aerated concrete therein and allowing the materials to rise and stiffen into a body. The former may also include the autoclave downstream from the mold for curing the body, and a divider downstream from the autoclave for dividing the cured body into a plurality of cured sheets to serve as the core material.
In this embodiment, the former may further comprise a conveyor and a sheet handler cooperating therewith for joining a plurality of the cured sheets together in end-to-end relation while advancing the cured sheets along a path of travel. The former may also secure the at least one face layer while the cured sheets are advanced along the path of travel.
In accordance with another embodiment, the former may comprise a mold downstream from the mixer, a divider downstream from the mold for dividing the body into a plurality of uncured sheets, and the autoclave downstream from the divider for curing the uncured sheets to serve as the core material. In this embodiment as well, the former may further comprise a conveyor and a sheet handler cooperating therewith for joining a plurality of the cured sheets together in end-to-end relation while advancing the cured sheets along a path of travel. The former may also secure the at least one face layer while the cured sheets are advanced along the path of travel.
In yet another embodiment, the former may comprise the mold, and the divider downstream from the mold. However, the uncured sheets may serve as the core material to which the at least one face layer is secured. Accordingly, the autoclave may be downstream from the divider, and preferably, after the cutter.
Still another embodiment of the system provides for near continuous production. In this embodiment, the former may comprise a dispenser and a conveyor cooperating therewith for dispensing the materials for making aerated concrete adjacent at least one face layer as the at least one face layer is advanced along a path of travel, and the autoclave downstream from the dispenser for curing the materials for making aerated concrete. The autoclave may preferably be after the cutter, for example.
In any of the embodiments, the former may secure first and second face layers on respective first and second major surfaces of the core material. For wallboard sheets, the at least one face layer supply may comprise at least one paper face layer supply. For backerboard sheets, the at least one face layer supply preferably comprises at least one moisture-resistant face layer supply.
The former may also include a bevel shaper for forming the first major surface of the core material to have beveled portions adjacent respective opposing longitudinal side edges. The former may also include an edge wrapper for securing the at least one face layer to extend around the opposing longitudinal side edges. In addition, the system may also include a reinforcing fiber supply cooperating with the mixer for adding reinforcing fibers to the materials for making aerated concrete.